HMC856 Eval board Interfacing

Hi,

One way to do is connect positive ports B0-B4 to a fixed voltage with a resistance, say 1.2k to GND and connect transistor switches to negative ports(B0~B4) with 2.7kohms each. Transistor switches can either be open or short to Vee. This way (B0-B4) change state. LVTTLs can drive switch transistors. 

If you supply shift the part between 3.3V and GND, and if LVTTLs can supply enough current, you wouldnt need interfacing transistors/level shifters. The RF signal though should be AC couple in that case. 

Sinan 

Hi,

I saw the HMC856 Eval board schematic (page 12 of the datasheet) and the B0-B4 ports are connected differently.

The positive ports B0-B4 are connected singularly to a test point with a 2.7KOhm resistor while the negative ports B0-B4 are connected together with 1.2KOhm to a test point. Your suggestion is not applicable to HMC856 Eval board. Is it correct?

Could you help me to understand the right way to management the B0-B4 ports of the HMC856 Eval board?

Could you help me to understand the right way to management the B0-B4 ports of the HMC856 with LVTTL signals?

Best Regards,
Daniele 

Control pins have internal 600ohms and there is a voltage division with externally connected resistors which are pulled down to -3.3V.

• J5 has jumpers on it, pulling down B0+~B4+ (positive pins) to -3.3V with 2.7k or not. With the internal 600ohm pull-up, positive pins are either set to -600mV(jumper installed) or 0mV(jumper not installed)
• As for the negative pins, 5 control pins are connected in parallel with an equivalent pull-up of 120ohms(600/5). With the external pull-down(1.2k), negative pins are set to -300mV. This jumper is not meant to be removed, it should always be on
• Thus, negative pins set to -300mV, positive pins are set to 0mV or -600mV. The differential control voltage is +300mV or -300mV.

Hi,

in the eval board, the 600 Ohm internal pull ups are connected to VT. The VT-J8 pin is floating (I didn't see a specific interconnection) while you supposed that this pin is connected to GND. It is correct?

Best Regards,

Daniele

VT should be tied to GND, you are correct.